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Maintaining cruise altitude while depressurised

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Maintaining cruise altitude while depressurised

Old 11th Mar 2016, 20:21
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Maintaining cruise altitude while depressurised

There is an airline over the last 3 months that has maintained a procedure on certain routes at cruise altitudes up to 41000ft, that if a depressurisation occurs, cruise altitude must be maintained until the completion of a 180 degree turn (over 4 mins at 480 knots).
This has recently been discontinued but I am interested in any comments and whether any other airlines around the world would or have entertained such a procedure.
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Old 12th Mar 2016, 00:57
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Where's the location that requires that?
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Old 12th Mar 2016, 05:29
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Legal (certification) requirement is to commence an emergency descend within one minute.
Any more time would require an approval, for that an analysis of the available oxygen would be required.
Another constraint are the passenger oxygen masks. Most are effective only below 25000 ft so the time to get there is limited.
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Old 12th Mar 2016, 06:10
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Most are effective only below 25000 ft so the time to get there is limited.
That's the first time I've ever heard that. Where do you get your information?
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Old 12th Mar 2016, 06:13
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This has recently been discontinued but I am interested in any comments and whether any other airlines around the world would or have entertained such a procedure.
I'm not surprised. That would surely be quite an effective way of making sure you had killed all your passengers!
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Old 12th Mar 2016, 06:31
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I don't recall the exact altitude, but from what I remember from altitude chamber classes while in the Air Force, one has to "pressure breath" 100% O2 when the ambient pressure drops below a certain level.

Only the cockpit masks are designed to do this.

The passenger masks are not designed, nor are able, to force oxygen under pressure through the lungs and into the hemoglobin above a certain pressure level.

I seem to remember that the critical level below which the passenger masks start to become effective is somewhere around 30,000 ft. (could be mistaken)

Last edited by wanabee777; 12th Mar 2016 at 08:32.
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Old 12th Mar 2016, 06:44
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30,000'? IRC
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Old 12th Mar 2016, 06:46
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Cockpit oxygen masks are not pressure masks. They are capable of a slight positive flow for the purpose of keeping smoke out of the mask and goggles but they do not provide pressurized o2 to the lungs.
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Old 12th Mar 2016, 06:51
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30,000 ft sounds about right.

Obviously, you would want to descend well below that level for the flight attendants and passengers to get adequate amounts of O2 into their blood stream.
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Old 12th Mar 2016, 06:54
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Cockpit oxygen masks are not pressure masks. They are capable of a slight positive flow for the purpose of keeping smoke out of the mask and goggles but they do not provide pressurized o2 to the lungs.
That's news to me.
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Old 12th Mar 2016, 07:14
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Likewise wanabee

Certainly the placard on the regulator our 777 flightcrew Eros masks states that pressure breathing is available up to 35?-?40K . Not at work at the moment so can't check the exact figure.
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Old 12th Mar 2016, 07:36
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The airbus Eros masks are not pressure masks.....but they mix ambient and oxygen below approx 33,000 feet - providing 100% oxygen above this level. I think this is what the previoys respondents are thinking about.
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Old 12th Mar 2016, 07:37
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So the temperature has plunged to circa -55 deg C and you're going to sit there for 4 minutes - give me a break - sheer self survival shouts go down!
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Old 12th Mar 2016, 07:48
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Pressure breathing equipment requires a different training regime. You do not, and will not, have pressure breathing equipment on an aeroplane for which you are not trained in its use. You have a mask that has an overpressure for the smoke scenarios and it provides 100% oxygen above approx 30000 feet. It mixes this with ambient below this level.

These masks increase the amount of O2 available to you and do NOT work by increasing the pressure of the O2 to get it into your haemoglobin. It is the partial pressure of the O2 within the gas (atmosphere) that does this. The O2 partial pressure decreases as we climb, which is why more O2 is required. We are NOT pressure breathing in a decompression.
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Old 12th Mar 2016, 08:02
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Maybe I'm confusing the present day O2 regulators with the ones we used to have on the 727.
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Old 12th Mar 2016, 08:14
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Very much doubt that. You will need to have done a course on pressure breathing if it were fitted. It isnt the sort of thing that you learn 'on the job' when you have just depressurised.
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Old 12th Mar 2016, 08:16
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Originally Posted by misd-agin View Post
Where's the location that requires that?
I'm reluctant to say due to repercussions but interested to know if any other airlines did it and what the forum thinks of the idea.
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Old 12th Mar 2016, 08:18
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Originally Posted by Stan Woolley View Post
I'm not surprised. That would surely be quite an effective way of making sure you had killed all your passengers!
That was my view. Not all, but some.
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Old 12th Mar 2016, 08:25
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Proper pressure breathing kit requires you to forcibly breath out against a lot more positive pressure than is provided by airline O2 masks. The stuff on airliners, whilst it might be called pressures breathing, most definitely isn't.
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Old 12th Mar 2016, 08:28
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The only courses I ever had involving pressure breathing O2 were over 40 years ago when we were required to go to the altitude chamber every 2 or 3 years while I was in the military. No training, in that regard, with my airline.

I don't recall the act of "pressure breathing" O2 to be all that complicated or involved.
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